Radiation therapy (RT) is a popular and efficient method for cancer treatment, where ionizing radiation is used in an attempt to destroy malignant tumor cells or to slow down their growth. RT is often combined with surgery, chemotherapy, or hormone therapy, but may also be used as a primary therapy mode. Radiation therapy is most commonly administered as external beam RT, which typically involves directing beams of radiated particles produced by sources located externally with respect to the patient or subject to the afflicted treatment area. The beam can consist of photons, electrons, protons or other heavy ions. As the beam travels through matter (e.g., the subject), energy from the ionizing radiation is deposited along the path in the surrounding matter. This energy is known as “dose,” and is used to measure the efficacy and accuracy of a radiation beam. Malignant cells are damaged along the path of radiation beam during the RT. Unfortunately, the damage from the radiation is not limited to malignant cells and may be incurred by any interceding or adjacent cells. Thus, the dosage of radiation to healthy tissues outside the treatment volume is ideally minimized to avoid being collaterally damaged.
Proton therapy is one type of external beam radiation therapy, and is characterized for using a beam of protons to irradiate diseased tissue. The chief advantage of proton therapy over other particle-based therapies is the ability to administer treatment dosages three dimensionally, by specifying the depth (i.e., penetration) of applied radiation, thereby limiting the inadvertent exposure of untargeted cells to the potentially harmful radiation. This enables proton therapy treatments to more precisely localize the radiation dosage when compared with other types of external beam radiotherapy. During proton therapy treatment, a particle accelerator, such as a cyclotron, is used to generate a beam of protons from an internal ion source located in the center of the cyclotron. Typically, a cyclotron is located in a location remote from the target treatment room. The generated protons are directed, via magnets, through a series of interconnecting tubes (called the beamline), and applied to a subject in a target treatment room.
Generally speaking, cyclotrons generate a proton beam at a fixed energy for the duration of a proton therapy treatment. During typical proton radiation treatments however, irradiating a tumor often requires irradiating an entire volume (a tumor, for example) at different depths within a patient or treatment subject. These depths, which may be referred to in discrete units as layers, naturally correspond to different “optimal” energy levels. Since cyclotrons operate only at a fixed energy during a treatment session, irradiating different depths can become problematic. Conventional methods for irradiating a volume are performed by applying a single beam current, and begin by targeting the furthest depth within a patient or subject. For differing depths, a component (such as a carbon filter or “degrader”) is inserted into the path of the extracted beam at some distance from the cyclotron. The degrader material reduces the speed of the particles (and thereby the beam energy). Every time the proton beam's energy is changed this results in a new “layer” within the patient or target receiving treatment.
However, the degrader material also reduces the density and number of particles comprising the beam (e.g., the “beam intensity”) that continues past the degrader. In order to achieve proper dose rates for each layer, this may be compensated by increasing the beam intensity that the cyclotron delivers to the degrader input. Unfortunately, using conventional techniques the change of beam intensity within a cyclotron can take a significant amount of time.
As a result, proton therapy according to conventional operating techniques is generally limited to relatively simple treatment plans, which even then may require exceptionally and inefficiently long irradiation times. In some cases, if the extracted beam current must be frequently varied according to a multiplicity of layers requiring treatment for example, new, practically separate treatment plans would need to be devised which would likely lead to even more delays and inefficiencies. Moreover, due to the complexity of the underlying machines, their operating and maintenance procedures, and the gravity of the corresponding medical procedures, highly trained and skilled operators are needed to perform the calculations and actions necessary to make adjustments to a proton beam current. Naturally, this can result in further inefficiency, delays or even potential hazards if qualified operators are not available.